Dual-tuned vibration damper

ABSTRACT

A driveline with a shaft and a vibration damper coupled to the shaft. The damper includes a hub, a first mass, a first resilient coupling, a second mass, and a second resilient coupling. The first mass is disposed concentrically about the hub. The first resilient coupling resiliently couples the first mass to the hub. The first resilient coupling has a first spring constant. The second mass is disposed concentrically about the first mass. The second resilient coupling resiliently couples the second mass directly to the first mass. The second resilient coupling has a second spring constant that is less than the first spring constant. The first mass and the first resilient coupling are configured to attenuate vibration at a first frequency. The second mass and the second resilient coupling are configured to attenuate vibration at a second frequency. The second frequency is lower than the first frequency.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 12/259,461 filedOct. 28, 2008, now U.S. Pat. No. 7,942,229, the disclosure of which isincorporated by reference as if fully set forth in detail herein.

FIELD

The present disclosure relates to a dual-tuned vibration damper and adriveline employing a dual-tuned vibration damper.

BACKGROUND

This section provides background information related to the presentdisclosure which is not necessarily prior art.

Vibration dampers are commonly used with rotating shafts or other rotarycomponents in a power transmission system, such as a crankshaft of aninternal combustion engine. The purpose of such vibration dampers is todamp the torsional vibrations at a specific frequency that is associatedwith the vibrations caused by the cyclic forces applied to the rotarycomponents during rotation.

In automotive vehicles that transmit rotary power from a powertrain to arear axle via a propshaft, it is possible for the propshaft to transmitvibration at a first frequency to the rear axle (from the powertrain)and to transmit vibration at a second, different frequency to thepowertrain (from the rear axle). It was relatively commonplace to alterthe operational characteristics of the powertrain (e.g., the torqueconverter or the transmission) to attenuate vibrations transmitted fromthe powertrain to the propshaft, as well as to employ a vibration damperto dampen vibrations transmitted from the rear axle to the propshaft. Assuch alterations to the operational characteristics of the powertraincan adversely affect the mileage of a vehicle, there is increasingresistance on the part of original equipment manufacturers to make suchalterations. Consequently, it is increasingly necessary for designers ofvehicle drivelines to deal with multiple sources of vibration in thevehicle driveline.

One approach that we have considered includes the use of a firstvibration damper that is coupled to a first side of the vehiclepropshaft for attenuating vibration at the first frequency, and a secondvibration damper that is coupled to a second side of the vehiclepropshaft for attenuating vibration at the second frequency. While suchsolution can be effective in some situations, we noted that there isconsiderable cost associated with the provision and installation of twodiscrete vibration dampers. Moreover, it would not be possible in somesituations to integrate two discrete dampers into the vehicle driveline.

SUMMARY

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

In one form, the present disclosure provides a method for dampingvibrations in a power transmission system. The power transmission systemincludes a first power transmitting component, a second powertransmitting component and a shaft that is adapted to transmit rotarypower between the first and second power transmitting components. Themethod includes: identifying a first frequency associated with vibrationtransmitted from the first power transmitting component to the shaft;identifying a second frequency associated with vibration transmittedfrom the second power transmitting component to the shaft, the secondfrequency being different from the first frequency; and coupling adamper to the shaft, the damper including a hub, a first mass, a secondmass, a first resilient coupling, and a second resilient coupling, thefirst mass being disposed concentrically about the hub, the second massbeing disposed concentrically about the hub and the first mass, thefirst resilient coupling resiliently coupling the first mass to the hub,the second resilient coupling resiliently coupling the second massdirectly to the first mass. The first mass and the first resilientcoupling are configured to attenuate vibration at a higher one of thefirst and second frequencies. The second mass and the second resilientcoupling are configured to attenuate vibration at a lower one of thefirst and second frequencies.

In another form, the present disclosure provides a method for dampingvibrations in a power transmission system. The power transmission systemincludes a first power transmitting component, a second powertransmitting component and a shaft that is adapted to transmit rotarypower between the first and second power transmitting components. Themethod includes: identifying a first frequency associated with vibrationtransmitted through the shaft; identifying a second frequency associatedwith vibration transmitted though the shaft, the second frequency beinglower than the first frequency; and coupling a damper to the shaft, thedamper including a hub, a first mass, a second mass, a first resilientcoupling and a second resilient coupling, the first mass being disposedconcentrically about the hub, the second mass being disposedconcentrically about the hub and the first mass, the first resilientcoupling resiliently coupling the first mass to the hub, the secondresilient coupling resiliently coupling the second mass directly to thefirst mass. The first mass and the first resilient coupling areconfigured to attenuate vibration at the first frequency. The secondmass and the second resilient coupling are configured to attenuatevibration at the second frequency.

In yet another form, the present disclosure provides a vibration dampercomprising a hub, a first mass, a first resilient coupling, a secondmass, and a second resilient coupling. The first mass is disposedconcentrically about the hub. The first resilient coupling resilientlycouples the first mass to the hub. The first resilient coupling has afirst spring constant. The second mass is disposed concentrically aboutthe first mass. The second resilient coupling resiliently couples thesecond mass directly to the first mass. The second resilient couplinghas a second spring constant that is less than the first springconstant. The first mass and the first resilient coupling are configuredto attenuate vibration at a first frequency. The second mass and thesecond resilient coupling are configured to attenuate vibration at asecond frequency. The second frequency is lower than the firstfrequency.

In a further form, the present disclosure provides a driveline thatincludes a shaft and a damper. The shaft is configured to couple a firstdriveline component to a second driveline component to transmit rotarypower therebetween. The damper dampens vibration transmitted through theshaft that occurs at a first frequency and at a second frequency that islower than the first frequency. The first frequency is associated with afirst vibration source in the driveline, while the second frequency isassociated with a second vibration source in the driveline that is notassociated with the first vibration source. The damper includes a hub, afirst mass, a second mass, a first resilient coupling and a secondresilient coupling. The hub is mounted to the shaft for rotationtherewith. The first mass is disposed concentrically about the hub. Thesecond mass is disposed concentrically about the hub and the first mass.The first resilient coupling resiliently couples the first mass directlyto the hub. The second resilient coupling resiliently couples the secondmass directly to the first mass. The first mass and the first resilientcoupling are configured to attenuate vibration at the first frequency.The second mass and the second resilient coupling are configured toattenuate vibration at the second frequency.

In still another form, the present disclosure provides a driveline thatincludes a shaft and a damper. The shaft is configured to couple a firstdriveline component to a second driveline component to transmit rotarypower therebetween. The damper dampens vibration transmitted through theshaft that occurs at a first frequency and at a second frequency that islower than the first frequency. The first frequency is associated with afirst vibration source in the driveline, while the second frequency isassociated with a second vibration source in the driveline that is notassociated with the first vibration source. The damper includes a hub, afirst mass, a second mass, a first resilient coupling and a secondresilient coupling. The hub is mounted to the shaft for rotationtherewith. The first mass is disposed concentrically about the hub. Thesecond mass is disposed concentrically about the hub and the first mass.The first resilient coupling resiliently couples the first mass to thehub. The second resilient coupling resiliently couples the second massdirectly to the first mass. The first mass and the first resilientcoupling are configured to attenuate vibration at the first frequency.The second mass and the second resilient coupling are configured toattenuate vibration at the second frequency

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

FIG. 1 is a schematic illustration of an automotive vehicle having avibration damper constructed in accordance with the teachings of thepresent disclosure;

FIG. 2 is a front elevational view of the vibration damper of FIG. 1;

FIG. 3 is a sectional view taken along the line 3-3 of FIG. 2;

FIGS. 4 and 5 are front elevational views of other vibration dampersconstructed in accordance with the teachings of the present disclosure;and

FIG. 6 is a schematic illustration similar to that of FIG. 1 butillustrating the vibration damper as mounted in a different location.

Corresponding reference numerals indicate corresponding parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION

Example embodiments will now be described more fully with reference tothe accompanying drawings.

Example embodiments are provided so that this disclosure will bethorough, and will fully convey the scope to those who are skilled inthe art. Numerous specific details are set forth such as examples ofspecific components, devices, and methods, to provide a thoroughunderstanding of embodiments of the present disclosure. It will beapparent to those skilled in the art that specific details need not beemployed, that example embodiments may be embodied in many differentforms and that neither should be construed to limit the scope of thedisclosure. In some example embodiments, well-known processes,well-known device structures, and well-known technologies are notdescribed in detail.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting. As usedherein, the singular forms “a”, “an” and “the” may be intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. The terms “comprises,” “comprising,” “including,” and“having,” are inclusive and therefore specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof. The method steps, processes, and operations described hereinare not to be construed as necessarily requiring their performance inthe particular order discussed or illustrated, unless specificallyidentified as an order of performance. It is also to be understood thatadditional or alternative steps may be employed.

When an element or layer is referred to as being “on”, “engaged to”,“connected to” or “coupled to” another element or layer, it may bedirectly on, engaged, connected or coupled to the other element orlayer, or intervening elements or layers may be present. In contrast,when an element is referred to as being “directly on,” “directly engagedto”, “directly connected to” or “directly coupled to” another element orlayer, there may be no intervening elements or layers present. Otherwords used to describe the relationship between elements should beinterpreted in a like fashion (e.g., “between” versus “directlybetween,” “adjacent” versus “directly adjacent,” etc.). As used herein,the term “and/or” includes any and all combinations of one or more ofthe associated listed items.

Although the terms first, second, third, etc. may be used herein todescribe various elements, components, regions, layers and/or sections,these elements, components, regions, layers and/or sections should notbe limited by these terms. These terms may be only used to distinguishone element, component, region, layer or section from another element,component, region, layer or section. Terms such as “first,” “second,”and other numerical terms when used herein do not imply a sequence ororder unless clearly indicated by the context. Thus, a first element,component, region, layer or section discussed below could be termed asecond element, component, region, layer or section without departingfrom the teachings of the example embodiments.

Spatially relative terms, such as “inner,” “outer,” “beneath”, “below”,“lower”, “above”, “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. Spatiallyrelative terms may be intended to encompass different orientations ofthe device in use or operation in addition to the orientation depictedin the figures. For example, if the device in the figures is turnedover, elements described as “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the example term “below” can encompass both an orientation ofabove and below. The device may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein interpreted accordingly.

With reference to FIG. 1 of the drawings, an automotive vehicle 10 isschematically illustrated as including a driveline 12 that is drivablevia a connection to a powertrain 14. The powertrain 14 can include anengine 16 and a transmission 18. The driveline 12 can include apropshaft 20, a rear axle assembly 22 and a plurality of wheels 24. Theengine 16 can be mounted in an in-line or longitudinal orientation alongthe axis of the vehicle 10 and its output can be selectively coupled tothe input of the transmission 18 to transmit rotary power (i.e., drivetorque) therebetween. The input (not specifically shown) of thetransmission 18 can be commonly aligned with the output of the engine 16for rotation about a rotary axis. The transmission 18 can also includean output 18 a and a gear reduction unit 18 b. The gear reduction unit18 b can be operable for coupling the transmission input to thetransmission output 18 a at a predetermined gear speed ratio. Couplings20 a, such as universal joints and/or flexible couplings, can beincorporated into the opposite ends of the propshaft 20. A first end ofthe propshaft 20 can be coupled for rotation with the output 18 a of thetransmission 18, and a second, opposite end of the propshaft 20 can becoupled for rotation with an input pinion 22 a of the rear axle assembly22. Drive torque can be transmitted through the propshaft 20 to the rearaxle assembly 22 where it can be selectively apportioned in apredetermined manner to the left and right rear wheels 24 a and 24 b,respectively. A vibration damper 26 constructed in accordance with theteachings of the present disclosure can be coupled to the driveline 12.While the vibration damper 26 is illustrated as being coupled to theinput pinion 22 a, it will be appreciated that the location of thevibration damper 26 can be altered as desired. In this regard, thevibration damper 26 can be mounted to the output 18 a of thetransmission 18, to the propshaft 20 proximate the transmission 18, orto the propshaft 20 proximate the rear axle assembly 22 as shown in FIG.6.

With reference to FIGS. 2 and 3, the vibration damper 26 can include ahub 28, a first resilient coupling 30, a first mass 32, a secondresilient coupling 34, and a second mass 36. The hub 28 can include acentral aperture 27 that can be sized to receive an element of thedriveline 12 (FIG. 1), such as a tubular shaft member 29 of thepropshaft 20. The first mass 32 can define an aperture 31 into which thehub 28 can be received. The first resilient coupling 30 can resilientlycouple the first mass 32 to the hub 28. The first resilient coupling 30can directly contact the hub 28 and the first mass 32 and can have afirst spring constant k1. In the particular example shown, the firstresilient coupling 30 directly contacts the hub 28 about its full outercircumference and directly contacts the first mass 32 about the fullinner circumference of the aperture 31. It will be appreciated, however,that amount of contact between the first resilient coupling 30 and thehub 28 and/or the first mass 32 can be tailored to a desired degree andas such, the outer circumference of the hub 28, the inner circumferenceof the aperture 31 and/or the first resilient coupling 30 can beconstructed in a discontinuous manner. The second mass 36 can define anaperture 35 into which the first mass 32 can be received. The secondresilient coupling 34 can resiliently couple the second mass 36 directlyto the first mass 32. In the example provided, the second resilientcoupling 34 directly contacts the first mass 32 along its full outercircumference and directly contacts the second mass 36 along the fullinner circumference of the aperture 35. It will be appreciated, however,that amount of contact between the second resilient coupling 34 and thefirst mass 32 and/or the second mass 36 can be tailored to a desireddegree and as such, the outer circumference of the first mass 32, theinner circumference of the aperture 35 and/or the second resilientcoupling 34 can be constructed in a discontinuous manner. The secondresilient coupling 34 can have a second spring constant k2 that isdifferent from the first spring constant k1. For example, the secondspring constant k2 can be less than the first spring constant k1. Thefirst and second resilient couplings 30 and 34 can be formed of adesired resilient material, such as an elastomer or thermoplasticelastomer.

The first mass 32 and the first resilient coupling 30 can be configuredto attenuate vibration at a first frequency f1. The second mass 36 andthe second resilient coupling 34 can be configured to attenuatevibration at a second frequency f2. The second frequency f2 can be lowerthan the first frequency f1. The first frequency f1 can be greater thanor equal to 250 Hertz and less than or equal to 600 Hertz. For example,the first frequency f1 can be greater than or equal to 300 Hertz andless than or equal to 500 Hertz. The second frequency f2 can be greaterthan or equal to 20 Hertz and less than or equal to 200 Hertz. Forexample, the second frequency f2 can be greater than or equal to 50Hertz and less than or equal to 150 Hertz.

With reference to FIGS. 1 and 2, a method for damping vibrations inaccordance with the teachings of the present disclosure is provided. Themethod can include identifying a first frequency f1 associated withvibration transmitted from a first power transmitting component, such asthe automotive transmission 18, to the propshaft 20; identifying asecond frequency f2 associated with vibration transmitted from a secondpower transmitting component, such as the rear axle assembly 22, to thepropshaft 20, the second frequency f2 being different from the firstfrequency f1; and coupling a vibration damper 26 to the propshaft 20.The vibration damper 26 can include a hub 28, a first mass 32, a secondmass 36, a first resilient coupling 30, and a second resilient coupling34. The first mass 32 can be disposed concentrically about the hub 28.The second mass 36 can be disposed concentrically about the hub 28 andthe first mass 32. The first resilient coupling 30 can resilientlycouple the first mass 32 to the hub 28. The second resilient coupling 34can resiliently couple the second mass 36 directly to the first mass 32.The first mass 32 and the first resilient coupling 30 can be configuredto attenuate vibration at a higher one of the first and secondfrequencies f1 and f2. The second mass 36 and the second resilientcoupling 34 can be configured to attenuate vibration at a lower one ofthe first and second frequencies f1 and f2.

Another method for damping vibrations in accordance with the teachingsof the present disclosure is provided. The method can includeidentifying a first frequency f1 associated with vibration transmittedthrough the propshaft 20; identifying a second frequency f2 associatedwith vibration transmitted though the propshaft 20, the second frequencyf2 being lower than the first frequency f1; and coupling a vibrationdamper 26 to the propshaft 20. The vibration damper 26 can include a hub28, a first mass 32, a second mass 36, a first resilient coupling 30,and a second resilient coupling 34. The first mass 32 can be disposedconcentrically about the hub 28. The second mass 36 can be disposedconcentrically about the hub 28 and the first mass 32. The firstresilient coupling 30 can resiliently couple the first mass 32 to thehub 28. The second resilient coupling 34 can resiliently couple thesecond mass 36 directly to the first mass 32. The first mass 32 and thefirst resilient coupling 30 can be configured to attenuate vibration atthe first frequency f1. The second mass 36 and the second resilientcoupling 34 are configured to attenuate vibration at the secondfrequency f2.

With reference to FIG. 4, another vibration damper 26 a constructed inaccordance with the teachings of the present disclosure is shown. Exceptas described herein, the hub 28 a, the first resilient coupling 30 a,and the first mass 32 a can be similar to the hub 28, the firstresilient coupling 30, and the first mass 32 described above andillustrated in FIGS. 2 and 3, respectively. The hub 28 a, the firstresilient coupling 30 a, and the first mass 32 a can cooperate to form atoothed interface 37.

In the particular example, the hub 28 a can have an outer hub surface38. The first mass 32 a can have an inner first mass surface 39. Aplurality of projections 40 can extend outward from the outer hubsurface 38 and can be received by corresponding recesses 45 formed onthe inner first mass surface 39, respectively. In the particular exampleprovided, four projections 40 and four corresponding recesses 45 areemployed, but those of skill in the art can appreciate that more orfewer projections 40 and recesses 45 could be employed. Each of theprojections 40 has a circumferentially extending portion 42 and at leasttwo radially extending portions 44. Each of the recesses 45 has acorresponding circumferentially extending portion 49 and at least twocorresponding radially extending portions 51. The first resilientcoupling 30 a can extend around and directly contact both the outer hubsurface 38 and the inner first mass surface 39. In the particularexample, the first resilient coupling 30 a is compressed between the twocircumferentially extending portions 42 and 49 and between the tworadially extending portions 44 and 51.

With reference to FIG. 5, yet another vibration damper 26 b constructedin accordance with the teachings of the present disclosure is shown.Except as described herein, the first mass 32 b, the second resilientcoupling 34 b, and the second mass 36 b can be similar to the first mass32, the second resilient coupling 34, and the second mass 36 describedabove and illustrated in FIGS. 2 and 3, respectively. The first mass 32b, the second resilient coupling 34 b, and the second mass 36 b cancooperate to form a toothed interface 41.

In the particular example, the first mass 32 b can have an outer firstmass surface 58. The second mass 36 b can have an inner second masssurface 43. A plurality of projections 60 can extend outward from theouter first mass surface 58 and can be received by correspondingrecesses 47 formed on the inner second mass surface 43, respectively. Inthe particular example provided, four projections 60 and fourcorresponding recesses 47 are employed, but those of skill in the artcan appreciate that more or fewer projections 60 and recesses 47 couldbe employed. Each of the projections 60 can have a circumferentiallyextending portion 62 and at least two radially extending portions 64.Each of the recesses 47 has a corresponding circumferentially extendingportion 53 and at least two corresponding radially extending portions55. The second resilient coupling 34 b can extend around and directlycontact both the outer first mass surface 58 and the inner second masssurface 43. In the particular example, the second resilient coupling 34b is compressed between the two circumferentially extending portions 62and 53 and between the two radially extending portions 64 and 55.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the invention. Individual elements or features ofa particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the invention, and all such modificationsare intended to be included within the scope of the invention.

What is claimed is:
 1. A driveline comprising: a shaft that is adaptedto couple a first driveline component to a second driveline component totransmit rotary power therebetween; and a damper for damping vibrationtransmitted through the shaft that occurs at a first frequency and at asecond frequency that is lower than the first frequency, the firstfrequency being associated with a first vibration source in thedriveline, the second frequency being associated with a second vibrationsource in the driveline that is not associated with the first vibrationsource, the damper comprising a hub, a first mass, a second mass, afirst resilient coupling and a second resilient coupling, the hub beingmounted to the shaft for rotation therewith, the first mass beingdisposed concentrically about the hub, the second mass being disposedconcentrically about the hub and the first mass, the first resilientcoupling resiliently coupling the first mass to the hub, the secondresilient coupling resiliently coupling the second mass directly to thefirst mass, wherein the first mass and the first resilient coupling areconfigured to attenuate vibration at the first frequency and wherein thesecond mass and the second resilient coupling are configured toattenuate vibration at the second frequency.
 2. The driveline of claim1, wherein the shaft comprises a tube and a universal joint coupled toan end of the tube.
 3. The driveline of claim 2, wherein the hub of thedamper is fixedly coupled to the tube.
 4. The driveline of claim 1,wherein the first resilient coupling has a first spring constant andwherein the second resilient coupling has a second spring constant thatis less than the first spring constant.
 5. The driveline of claim 1,wherein the second resilient coupling directly contacts both the firstand second masses.
 6. The driveline of claim 1, wherein the first andsecond resilient couplings are formed of a thermoplastic elastomer. 7.The driveline of claim 1, wherein the first driveline component is atransmission and wherein the second driveline component is an axleassembly.
 8. The driveline of claim 1, wherein the hub, the firstresilient coupling, and the first mass cooperate to form a firstinterface; wherein the first mass, the second resilient coupling, andthe second mass cooperate to form a second interface; and wherein atleast one of the first and second interfaces comprises a toothedinterface.
 9. A driveline comprising: a shaft that is adapted to couplea first driveline component to a second driveline component to transmitrotary power therebetween; and a damper for damping vibrationtransmitted through the shaft that occurs at a first frequency and at asecond frequency that is lower than the first frequency, the firstfrequency being associated with a first vibration source in thedriveline, the second frequency being associated with a second vibrationsource in the driveline that is not associated with the first vibrationsource, the damper comprising a hub, a first mass, a second mass, afirst resilient coupling and a second resilient coupling, the hub beingmounted to the shaft for rotation therewith, the first mass beingdisposed concentrically about the hub, the second mass being disposedconcentrically about the hub and the first mass, the first resilientcoupling resiliently coupling the first mass directly to the hub, thesecond resilient coupling resiliently coupling the second mass directlyto the first mass, wherein the first mass and the first resilientcoupling are configured to attenuate vibration at the first frequencyand wherein the second mass and the second resilient coupling areconfigured to attenuate vibration at the second frequency.
 10. Thedriveline of claim 9, wherein the shaft comprises a tube and a universaljoint coupled to an end of the tube.
 11. The driveline of claim 10,wherein the hub of the damper is fixedly coupled to the tube.
 12. Thedriveline of claim 9, wherein the first resilient coupling has a firstspring constant and wherein the second resilient coupling has a secondspring constant that is from less than the first spring constant. 13.The driveline of claim 9, wherein the second resilient coupling directlycontacts both the first and second masses.
 14. The driveline of claim 9,wherein the first and second resilient couplings are formed of athermoplastic elastomer.
 15. The driveline of claim 9, wherein the firstfrequency is greater than or equal to 250 Hertz and less than or equalto 600 Hertz.
 16. The driveline of claim 15, wherein the first frequencyis greater than or equal to 300 Hertz and less than or equal to 500Hertz.
 17. The driveline of claim 16, wherein the second frequency isgreater than or equal to 20 Hertz and less than or equal to 200 Hertz.18. The driveline of claim 17, wherein the second frequency is greaterthan or equal to 50 Hertz and less than or equal to 150 Hertz.
 19. Thedriveline of claim 9, wherein the second frequency is greater than orequal to 20 Hertz and less than or equal to 200 Hertz.
 20. The drivelineof claim 17, wherein the second frequency is greater than or equal to 50Hertz and less than or equal to 150 Hertz.
 21. The driveline of claim 9,wherein the hub, the first resilient coupling, and the first masscooperate to form a first interface; wherein the first mass, the secondresilient coupling, and the second mass cooperate to form a secondinterface; and wherein at least one of the first and second interfacesis a toothed interface.